1. Field of the Invention
The present invention generally relates to process control systems, and more specifically to a method and apparatus for displaying historical information related to field devices used in process control plants.
2. Related Art
A process control plant generally contains several field devices, which are controlled to implement a desired control process. To enable such control, each field device contains components such as sensors (which measure various variables such as temperature, flow, pressure, etc.), control elements (e.g., valves, switches), and transmitters (which transmit any desired information to a processing system, which controls the manufacturing process). For example, field devices containing pressure sensors may be monitored and valves controlled to maintain the pressure level in a boiler (in general equipment) at a desired value.
There has been a general recognised need to monitor the status of the field devices, at least during the operation of a plant. Typically, a monitoring system is provided to receive and display the status information. The monitoring system may contain a central server which receives the status information, and several client systems may be provided which retrieve and display the status information according to a suitable user interface.
Field device vendors often provide a device description (DD), which contains various information elements of interest. Each information element contains some or more of attributes such as the type (e.g., dynamic variable, static variable, menu, etc.) of the element, the identifier, label, description, relationship with other information elements, etc. In the embodiments described below, the relationships are defined to organize the information elements according to a tree structure, which can be hierarchically navigated to view the present values corresponding to desired information elements of interest.
The tree structure can be different at different time instances. For example, in the case of DDs noted above, different tree structures are valid for different values of a dynamic variable. The monitoring system generally displays a menu representing the tree structures and a user may navigate and select different information elements of interest from the displayed menu to view the corresponding value during operation of the plant.
There is also a general recognised need to view historical information relating to the status of field devices. It is desirable that a user be provided at least as much information as is being provided (or available) during the operation of the plant.